One can only guess at what debate preparation was like on both the D and R sides, but there's some more implicit information here than we usually get. TFG we know, no matter what kind of prep he gets, is just going to do his own thing because he thinks he knows better.
But on the D side we saw how Biden did vs. how Harris did, and they probably both received similar debate prep. Biden has a lot of good qualities, but being accurate and specific isn't among them.
+
And that's before you get to Biden's speech impediments and slowness of response due sickness and age. He's just always been a fuzzy candidate.
Kamala Harris was able to internalize the debate prep and make it fast, hard, and pointed: absorb, respond, counter-attack. And the contrast to both Biden and TFG couldn't be greater.
